1. Field of the Invention
The present invention relate to a wireless synchronous system, radio apparatuses, sensor devices, a wireless synchronizing method, and a non-transitory computer-readable recording medium.
2. Description of the Related Art
Conventional techniques are known, which use plural high-speed cameras synchronized with each other for continuously shooting fast-moving phenomena such as blasts, crashes, combustions, shocks, discharge, and the like. And also techniques are known, which use a video camera to record images of an athlete for purpose of sport training (for instance, golf), and use sensor devices attached onto the athlete to detect and record data.
A technique is disclosed in Japanese Unexamined Patent Publication No. 2009-296323, in which one master camera is connected to plural slave cameras, and a video synchronizing signal for a high-speed camera is transferred from the master camera to the plural slave cameras, whereby plural high-speed cameras are brought into synchronization for shooting one object.
In the above disclosed technique, the master camera is provided with a timing controlling unit for establishing an accurate synchronization among the master camera and the plural slave cameras. The timing controlling unit uses a pulse signal to measure an actual delay along a transmitting path and corrects such delay based on the result of the measurement. The technique is used for continuously shooting fast-moving phenomena such as blasts, crashes, combustions, shocks, discharge, and the like, and belongs to a class of high-speed cameras for very specific business use, which are capable of shooting at an extremely high rate of a million frames per second.
Japanese Unexamined Patent Publication No. Hei07-289676 discloses another technique, which uses a video camera(s) to record an image of the athlete and a sensor device (s) attached on the athlete to detect and record sensor data for purpose of analysis of golf playing motion.
The technique disclosed in the latter publication consists of a video camera(s) and a sensor device(s). The video camera has its own real time clock, and records a video image as well as a time code based on a real time counted by its own real time clock. Also, the sensor device has its own real time clock, and measures and records sensor data (grip strength) as well as time information based on a real time counted by its own real time clock. Then, both the information of the video camera and the information of the sensor device are compared, and the sensor data is displayed, which corresponds to the time coincident to the time code of the video image. As another example, the sensor device transfers a measured sensor signal by means of analog radio communication to an audio input of the video camera for shooting a video image and the video camera records the received sensor data together with the video image.
But the technique disclosed in Japanese Unexamined Patent Publication No. 2009-296323 requires users to prepare accurate and troublesome settings before performing the shooting operation, such as calculating a delay time for correction by using a pulse signal. Therefore, the technique has a disadvantage that is hard for the consumer users to use.
The method of measuring a delay, using the pulse signal has another disadvantage that an accurate measurement cannot be made because of uncertain delays caused due to sampling and/or packet operations in digital radio transmission, when said method is used to measure a delay along a radio transmission path.
An accurate delay along an analog transmission path can be measured, but communication only between one master apparatus and one slave apparatus can be made along the analog transmission path. Therefore, the master equipment is required to equip with the same number of radio units as number of slave apparatuses, which increases the system in scale and costs, consuming much energy.
In the technique disclosed by Japanese Unexamined Patent Publication No. Hei07-289676, differences between the clocks of the respective apparatuses are large. The technique cannot be used for synchronous shooting by plural high-speed cameras. The technique has a problem that sensor information cannot be obtained in synchronization with the images shot by the high-speed cameras. In the case where the analog radio transmission is used, only one sort of sensor data can be recorded, and therefore, the technique cannot be used for recording, for instance, three-dimensional data, X, Y, Z.